1. Field of the Invention
The present invention relates to electrically driven vehicles. In particular, the present invention relates to limiting motor performance in accordance with certain operating conditions of the vehicle.
2. Background Art
The present invention relates to electrically driven vehicles having “electric only” capabilities. Common “electric only” capable hybrids include a series hybrid electric vehicle (SHEV), a parallel hybrid electric vehicle (PHEV), and a parallel/series hybrid electric vehicle (PSHEV).
“Electric only” capable vehicles include at least two power sources, where one of the at least two power sources stores energy and one of the power sources generates energy. The “electric only” designation indicates the vehicle can be driven with energy from the energy storing power source (battery) if the energy generating power source (engine or fuel cell) is turned off or not generating power.
The energy storing power sources can be distinguished from the energy generating power source because the storing power source must receive energy, rather than generating its own energy. Common energy storing power sources are batteries and common energy generating power sources are engines and fuel cells which consume fuel and produce chemical reactions to generate the electric energy.
Each of the power sources can be used to provide torque to wheels for driving the vehicle. The software, electronics, and mechanism which permit the power sources to provide torque to the wheels are referred to as a drivetrain.
The drivetrain for the energy storing power source is referred to as an auxiliary drivetrain to distinguish it from the drivetrain for the energy generating power source which is referred to as a primary drivetrain. In this manner, the primary drivetrain includes the generating power source and the auxiliary drivetrain includes the storing power source.
A problem may arise if the primary drivetrain experiences a condition which limits or prevents it from providing torque to the wheels or providing power to the auxiliary drivetrain. Assuming that the hybrid vehicle only includes one primary drivetrain and the storing energy source in the auxiliary drivetrain is a battery, the continued driving of the vehicle may be limited to the amount of available battery energy remaining in the battery.
The continued driving of the vehicle then becomes dependent on the remaining battery energy and how the remaining energy is used by an electric driving motor used to drive the vehicle. Generally, it is desirable to control the use of the remaining battery energy to prolong vehicle driving. Accordingly, there is a need for a method of optimally controlling the HEV when the primary drivetrain is limited or unable to provide nominal performance.